1. Field of the Invention
The present invention relates generally to fluid filled vibration damping devices each designed to produce vibration damping effect based on the flow behavior of a non-compressible fluid sealed therein, and more particularly to a fluid filled type vibration damping device having a partition member positioned therein to form a plurality of fluid chambers, which chambers communicate with one another through fluid flow passages or the like.
2. Description of the Related Art
Fluid filled vibration damping devices capable of exhibiting vibration damping effect based on resonance or other flow action or behavior of a non-compressible fluid sealed therein are known in the art, as vibration damping devices, such as vibration damping support or vibration damping couplings, intended for installation between components that make up a vibration transmission system. U.S. Pat. No. 6,902,156 discloses one example of the vibration damping device of this kind, wherein a first mounting member is positioned next to one opening of a second mounting member of tubular shape, and the first mounting member and second mounting member are elastically connected by a main rubber elastic body. The device is used as an automotive engine mount, for example.
This type of fluid filled vibration damping device includes typically a plurality of fluid chambers provided therein, and fluid flow passages connecting these fluid chambers. Through appropriate adjustment of the passage length or cross section of the fluid flow passages, vibration damping effect based on resonance of other flow behavior of the fluid caused to flow through the fluid flow passages can be achieved against vibration in particular frequency band or bands to be damped.
As one type of structure for forming the multiple fluid chambers and fluid flow passages, such as that taught in U.S. Pat. No. 6,902,156, it is proposed to utilize a partition member that is secured fit internally into the second mounting member. This partition member has a recess which opens outward in the axial direction, with the opening of the recess being covered by a rubber elastic plate. By securing the partition member fit into the tubular section of the second mounting member, a primary fluid chamber is formed between the partition member and the main rubber elastic body, while an auxiliary fluid chamber is formed in the recess of the partition member. A fluid flow passage connecting the primary fluid chamber and the auxiliary fluid chamber is formed, utilizing the partition member.
It is further proposed to position a fastening member superposed against the partition member on the end face thereof where the opening of the recess is located, so that the rubber elastic plate is covered from the outside by this fastening member, thereby forming a working air chamber situated to the opposite side of the rubber elastic plate from the auxiliary fluid chamber. By forming this working air chamber, the rubber elastic plate can be prevented from interfering with other components thus protecting the rubber elastic plate, while at the same time permitting elastic deformation of the rubber elastic plate. Also, through appropriate adjustment of air pressure in the working air chamber for example, it is possible to adjust the spring rigidity, and hence the vibration damping characteristics, of the auxiliary liquid chamber, a portion of whose wall is constituted by the rubber elastic plate. It is further possible, as taught in U.S. Pat. No. 6,902,156, to efficiently ensure space for forming a variable-capacity equilibrium chamber, situated to the opposite side of the partition member from the working air chamber.
However, the inventors have recently found that with fluid filled vibration damping devices of such conventional design, it is difficult to achieve consistent tuning characteristics on the part of the fluid flow passages, creating the problem that variability of vibration damping characteristics tends to occur easily among products.
Research conducted by the inventors as to the cause of this problem led to the discovery that a significant cause of variability among products probably lies in the characteristics of the auxiliary fluid chamber, and particularly the spring rigidity of the auxiliary fluid chamber wall. Additional research showed that the movable rubber film which constitutes a part of the wall of the auxiliary fluid chamber is subjected to unanticipated strain and stress during the vibration damping device manufacturing process. Thus, even where the spring characteristics of the movable rubber films are the same prior to assembly, it may possibly occur that significant variability in the spring characteristics thereof may arise after assembly.
Specifically, during the process of fastening the movable rubber film at the outside peripheral edge thereof to the opening of the recess of the partition member in order to form the auxiliary fluid chamber, it is necessary to ensure a sufficient level of fluid-tightness both in the auxiliary fluid chamber formed to one side of the movable rubber film, and in the working air chamber formed to the other. Accordingly, in the conventional design disclosed in U.S. Pat. No. 6,902,156, a mounting fitting of ring shape is pre-attached to the outside peripheral face of the movable rubber film, and this mounting fitting is secured mating fluid-tightly with the partition member and the fastening member. Namely, a mating projection that projects out towards the recess of the partition member is formed on the fastening member, and the edge of one open axial end of the mounting fitting affixed to the outside peripheral face of the movable rubber film is fastened externally onto this mating projection portion. Then, when this fastening member is superposed against the partition member, the mounting fitting affixed to the outside peripheral face of the movable rubber film is secured press-fit into the opening of the recess of the partition member. Subsequently, the partition member and the fastening member that have been assembled together with the movable rubber film are positioned inserted within the tubular section of the second mounting member. In this state, the tubular section is subjected to a diameter-constricting process so as to attach them integrally fitting into the second mounting member.
However, during the process of fastening the partition member and the fastening member in state of being fitted into the second mounting member, it is difficult to maintain concentricity of the partition member and the fastening member, which were originally separate components. Consequently, in the course of the tubular section of the second mounting member being subjected to the diameter-constricting process, the partition member and the fastening member may shift out of position relative to each other in the axis-perpendicular direction. Thus, the mounting fitting, which is fastened respectively to both the partition member and the fastening member, undergoes deformation in association with this shifting out of position of the two members in the axis-perpendicular direction. As a result, there may be a loss of seal in areas of the mounting fitting that mate with the partition member and the fastening member, with a resultant possible drawback that sufficient fluid-tightness in the auxiliary fluid chamber or working air chamber cannot be assured. Also, it may possibly occur that the desired spring properties will not be attained due to deformation or stress of the movable rubber film, induced in the movable rubber film by deformation of the mounting fitting.